I have this code on my page _template:
[[[http://snippets.wdfiles.com/local--code/code:url-title-with-slash-redirect/1#http://mysite.wikidot.com/comment:new_comment/edit/true/parentPage/%%fullname%%/title/Re:%20%%title%% | Reply]]]
In the generated URL, the %%title%% expansion has the spaces escaped correctly and most of the time the created link is correct.
However if the title has a "%" character in it, that is not escaped, leading to a generated URL like this:
http://snippets.wdfiles.com/local--code/code:url-title-with-slash-redirect/1#http://mysite.wikidot.com/comment:new_comment/edit/true/parentPage/thread:834/title/Re:%20Expect%20a%2015%%20performance%20loss%20coming%20soon
Note the "%" after "15" is not escaped. The result is a 400 — Bad Request error.